Topic 4 – Atomic Structure Fundamentals Flashcards
whats the radius of an atom
1 x 10^-10 m
the radius of the nucleus is __________ the radius of the atom
less than 1/10000
where do we find electrons
energy levels
energy levels which are further from the nucleus are at a ____________ than those close to the nucleus
higher energy level
how can an electron change energy levels to move to a higher energy level
if the atom absorbs electromagnetic radiation
how can an electron change to a lower energy level?
if the atom emits electromagnetic radiation it can return to a lower energy level
What is the mass number
the larger number, protons + neutrons
why do atoms have no overall charge?
number of electrons is equal to number of protons
so negative charges in electrons cancels out positive charge in protons
whats the atomic number
number of protons/electrons
how to calculate neutrons?
subtract atomic number from mass number
whats an isotope
when atoms of the same element have diff nos of neutrons
what did the ancient greeks believe about atoms?
everything was made of atoms. atoms were tiny spheres which couldn’t be divided
why was the discovery of electrons important
it showed atoms are NOT spheres that can’t be divided. they have an internal structure.
what was the plum pudding model
ball of positive charge w/ negative electrons embedded in it
describe the finding of the alpha particle scattering experiment
most particles went straight through the gold meaning atoms are mostly empty space (pp models wrong)
some atoms were deflected meaning centre of the atom must have a positive charge that repelled the alpha particles
some particles bounced straight back so the mass of the atom must be concentrated in the centre.
what did scientists replace the plum pudding model with?
The nuclear model
what did niels bohr sugges t
electrons orbit the nucleus at specific distances (now called energy levels)
why was niels bohrs theory accepted?
Bohrs work agreed with the results of experiments by other scientists
what was the order of discovery?
electrons, protons, neutrons
what is radioactive decay
when isotopes have an unstable nucleus so the nucleus gives out radiation to become stable.
radioactive decay is a _____ process
random
what is activity and what unit is it measured in?
the rate at which a source of unstable nuclei decay
measured in becquerels (Bq)
1Bq = 1 decay per second
what is the countrate
the number of decays recorded each second by a detector .
whys the countrate different to activity?
Background radiation
whats an alpha particle
a helium nucleus
whats a beta particle
an electron which is ejected from the nucleus at a v high speed
how is a beta particle formed
inside a nucleus when a neutron changes into a proton and an electron
whats a gamma ray
type of electromagnetic radiation from the nucleus
whats alpha particles range in air
alpha particles are large meaning they can travel around 5cm before they collide w air particle and stop
how far can beta particles travel in air
beta particles can travel further than alpha,, they can travel 15cm before stopping
how far can gamma radiation travel
several metres before stopping (further than both alpha and beta)
what are alpha particles stopped by (penetration)
a single sheet of paper
what are beta particles stopped by
a few millimetres of aluminium (more penetrating than alpha)
what are gamma rays stopped by
several cm of lead (most penetrating)
what does ionising mean
when radiation collides with atoms, that can cause the atoms to lose electrons and form ions
what does it mean to be strongly ionising
can produce a lot of ions when colliding with material
order of ionising ability:
alpha: v strongly ionising
beta: quite strongly ionising
gamma: weakly ionising
during alpha decay the atomic number____
decreases by 2
during alpha decay the mass number ____
decreases by 4
during beta decay the atomic number____
increases by 1
during beta decay the mass number ____
does not change
in gamma decay, both atomic number and mass number______
do not change
what is the half life
the time it takes for the number of nuclei of an isotope in a sample to halve.
OR
the time it takes for the count rate (or activity) from a sample containing an isotope to fall to half its initial level
whats the risk of ionising radiation
can increase the risk of cancer in humans
what is Irradiation?
irradiation is exposing an object to nuclear radiation (eg sterilisation)
why would an object that needs to be sterilised be placed in a plastic wrapper?
to stop bacteria from entering after sterilisation
when using gamma radiation to sterilise an object, why would you use a lead shield?
to protect the workers
how does gamma radiation sterilise objects?
by killing any bacteria present
why does an object thats been sterilised with gamma rays NOT become radioactive?
Objects come into contact w/ radiation but not radioactive isotope itself
what type of shielding of shielding should you use for the types of radiation
alpha- gloves
beta & gamma- lead apron
(lead walls / lead- glass screen)
what can we use a radiation monitor for
to measure how much radiation a person has received so we can stop them from working with radioactive isotopes
whats radioactive contamination?
when unwanted radioactive isotopes end up on other materials
why is radioactive contamination hazardous?
atoms decay and emit ionising radiation
when would alpha radiation be very damaging?
if inhaled or swallowed
what are the natural sources of background radiation
certain rocks including granite. (Cornwall suffers)
cosmic rays
what are cosmic rays
cosmic rays are v high energy particles which travel through space and crash into earths atmosphere
what are the man made background radiation examples
nuclear weapon testing
nuclear accidents
what can your exposure to BR be affected by
location and occupation
to check the function of the thyroid gland, what does the patient drink?
solution of radioactive iodine
what does radioactive iodine emit?
gamma radiation which passes out of the body and can be detected
what are the issues to consider when using a radioactive tracer
must emit radiation that can pass out of the body and be detected , must not be strongly ionising so it doesn’t cause damage, must not decay into another radioactive isotope and must have short half life so isnt in body for long time.
whats the benefit of using a radioactive rod to treat cancer?
placed very precisely next to tumour and there’s less damage to healthy tissue
what is nuclear fission?
when the nucleus absorbs a neutron, it splits, forming two daughter nuclei , emitting two or 3 neutrons + gamma radiation & releases energy
what happens to the neutrons emitted during fission?
can now be absorbed by more uranium nuclei and trigger fission again (eventually called chain reaction)
what is an explosion in a nuclear weapon caused by?
uncontrolled fission chain reaction
whats a controlled chain reaction used for
releasing energy in a nuclear reactor
what happens in nucleur fusion
2 light nuclei join to form a heavier nucleus. Some of the mass of the nuclei can be converted into energy which is released as radiation. NOT. a chain reaction
